Fallopia ×moravica (Polygonaceae), a new hybrid between Fallopia compacta and F. sachalinensis

A new knotweed hybrid originating from the crossing of Fallopia compacta and F. sachalinensis is described based on plant material collected in the Moravia region in the Czech Republic as F. ×moravica. In addition to the Czech Republic, the hybrid has also been reported previously from the United Kingdom and New Zealand; however, it was not distinguished from F. ×bohemica, a hybrid between F. japonica and F. sachalinensis, since its one parent (F. compacta) has been generally treated only as a variety of F. japonica. F. ×moravica differs from the morphologically most similar hexaploid (2n = 6x = 66) F. ×bohemica by its tetraploid (2n = 4x = 44) number of chromosomes and by the constant absence of purple spots on stem internodes (which are usually present in F. ×bohemica). The new hybrid also differs from F. ×bohemica as well as other European Fallopia members by its unique relative genome size. Other potential morphological and cytological differences of F. ×moravica from the related F. ×bohemica are discussed.